On a gas range or under a broiler, roast the green, red and poblano peppers until well charred. Let cool. Stem and seed the charred peppers. Coarsely chop and set aside.
In a spice grinder or with a mortar and pestle, finely grind the whole guajillo and pasilla chiles and set aside.
In a large saucepan, warm the oil over medium heat. Add the onions and cook, covered, 3 to 5 minutes. Add the guajillo and pasilla chiles, cumin, chili powder, oregano, thyme, black pepper, salt and garlic. Stir and cook until the spices become fragrant and are fully coated in oil, 3 to 5 minutes.
Add the tomatoes, green chiles and sugar. Stir and continue to cook until the sauce starts to simmer. Reduce the heat to medium-low and continue to cook until the vegetables soften and the flavors come together, 30 to 40 minutes. Taste and add additional salt and pepper as needed.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Lone Star Taco Bar, Allston, Massachusetts